Field of the Invention
The present invention relates to a magnetic-disk glass substrate.
Background Information
Nowadays, in order to record data, hard disk drives are incorporated in personal computers, laptop computers, DVD (digital versatile disc) recording apparatuses, and the like. In particular, a magnetic disk obtained by providing a magnetic layer on a non-magnetic substrate for a magnetic disk is used in a hard disk drive used in a device for which portability is a prerequisite, such as a laptop personal computer. A glass substrate is used as a magnetic-disk substrate, for example.
In order to meet the demand for an increase in the recording density and an increase in the storage capacity of magnetic disks, DFH (disk flying height)-type magnetic heads (referred to as DFH heads, hereinafter) have been developed in which, due to allowing only a recording and reproduction element (at least one of a recording element and a reproduction element to protrude toward the medium surface, a distance between the magnetic disk surface and the recording and reproduction element (referred to as a flying height, hereinafter) is shorter than in a conventional magnetic disk, and a flying height of about 5 nm is achieved, for example.
In such DFH heads, the above-described flying height is short, and thus it is necessary to avoid attachment of minute particles and the like to main surfaces of magnetic disks. In order to suppress the attachment of these minute particles, it is desirable that not only main surfaces but also edge surfaces of the glass substrate are polished with high precision, so that defects such as minute recesses and the like are not formed.
Usually, the edge surface of a glass substrate includes a side wall surface of the glass substrate and chamfered surfaces provided between this side wall surface and the main surfaces. In this glass substrate, a glass substrate that has no recessed pit defects on chamfered surfaces is known (JP 2012-142084A).
The glass substrate is obtained by performing edge surface polishing using a polishing brush after chamfering processing is performed with a grindstone to which diamond abrasive particles are fixed, and is a glass substrate having five or less pit defects/mm2, the pit defects having a diameter or a major length of 10μm or more that are observed after the surface of the chamfered surfaces of the glass substrate are etched by 5μm.